As technological development and a need for mobile instruments have increased, a demand for secondary batteries as energy sources has increased rapidly. Among such secondary batteries, lithium secondary batteries having high energy density and voltage, long cycle life and a low discharging rate have been commercialized and used widely. A lithium secondary battery includes a positive electrode, a negative electrode and a separator interposed between the positive electrode and the negative electrode, and the electrode, such as a positive electrode or negative electrode, is obtained by applying electrode slurry containing an electrode active material, binder and a solvent to an electrode current collector, and carrying out drying and rolling.
Recently, as the attention to environmental problems has increased, there has been grown the market of systems using a high-capacity battery, such as electric vehicles and hybrid electric vehicles capable of substituting for vehicles using fossil fuel, including gasoline vehicles and diesel vehicles, one of the main causes of air pollution. In addition, as a power source for such systems, there is a need for designing a high-capacity electrode for manufacturing a lithium secondary battery having high energy density, high output and high discharge voltage.
In the market, a high-loading electrode is evaluated as a loading amount of at least 950 mg/25 cm2 or more on the positive electrode basis and a loading amount of at least 500 mg/25 cm2 or more on the negative electrode basis. There has been an attempt to increase the amount of an electrode active material to design a high-loading electrode and thus a high-loading electrode having a large thickness of electrode active material layer has been suggested. However, such an electrode having a large thickness of electrode active material layer requires a relatively increased drying temperature during the manufacture of the electrode. Since the drying temperature is increased, a binder may be transported to the surface of the electrode active material layer, resulting in a problem of an increase in resistance of the electrode.
In addition, there is another problem in that such an increased thickness of electrode active material layer causes degradation of impregnation ability of an electrolyte, resulting in degradation of rate characteristics of a battery.